Large-Scale Meteorological Conditions Associated with Midlatitude, Mesoscale Convective Complexes

Abstract

Objective analyses of composited meteorological conditions attending ten Mesoscale Couvective Complexes (MCC) reveal a number of distinctive characteristics and important interactions with the large-scale environment. The systems appear to be linked to eastward progression of a weak, middle-tropospheric, short-wave trough. Initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low-level warm advection. The MCC system acquires mesoscale organization while it moves eastward ahead of the short-wave trough. Diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels. The mature MCC exhibits many similarities to tropical convective systems, although it occurs within a considerably different large-scale setting. Inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation. Thickness increases within this region produce anomalously high heights in the upper-troposphere above the MCC and intense outflow develops in the region where the height gradient has increased. Decay typically occurs as the system moves east of the region of conditionally unstable air and low-level warm advection. However, as the system decays, atmospheric response to residual temperature perturbations results in intensification of the precursor short-wave trough within the upper half of the troposphere.